Choroidal morphology under pachydrusen

Importance: To reveal choroidal morphological profiles under pachydrusen. Background: Drusen in pachychoroid disorders show certain differences from conventional drusen and are recently named as “pachydrusen.” This study analysed the specific choroidal morphology under pachydrusen. Design: This study is a cross-sectional case series. Participants: Enrolled were 136 eyes with pachydrusen from 134 patients. Methods: The presence of pachydrusen in fundus area covered by a 12 × 9 mm² optical coherence tomography (OCT) image was accessed in eyes with pachychoroid-related diseases or their fellow eyes using colour fundus photography and swept source OCT. Choroidal morphology under the pachydrusen was analysed using OCT B-scans and en face images. Main Outcome Measures: Choroidal thicknesses and topographical correlation between pachydrusen and pachyvessels. Results: A total of 225 pachydrusen in 136 eyes were analysed. The mean number of pachydrusen was 1.65 ± 1.07 per eye. Most pachydrusen were located para- or perifoveally (37 subfoveal, 86 parafoveal and 102 perifoveal). The proportion of Haller's layer to total choroidal thickness was higher at the area of the pachydrusen compared to the subfovea (0.881 ± 0.081 vs 0.765 ± 0.111, P < 0.001). In multimodal image analysis, 90.1% of pachydrusen identified using fundus photography and OCT B-scan were located at the area of a dilated Haller vessel (pachyvessel) seen on en face images. Conclusions and Relevance: Choroidal morphology under the pachydrusen showed increased Haller's layer thickness with an attenuated choriocapillaris layer, which is the hallmark of pachychoroid definition. Topographically, their locations correlated with the underlying pachyvessel.